1. Field of the Invention
The present invention relates to a magnetic image signal recording and playback apparatus in which a high definition image signal is converted into a video signal of NTSC or PAL system, etc., and the video signal is recorded.
2. Description of the Prior Art
With recent increase of display screen size and recent improvement on image definition, the Industry Standard High-Definition (referred to as "HD", hereinafter) TV system is developed and is wide spreading through satellite broadcastings, etc.
The number of effective video scanning lines of 1 frame in the HDTV system is 1035 which is about 2.2 times the number of effective video scanning lines of 1 frame in the NTSC system which is 480 and its field frequency is 60 Hz which is substantially equal to 59.94 Hz of the NTSC system. The resolution of the HD signal having frequency band of 20 MHz is about 1000 TV's/effective scanning lines (horizontal resolution) while that of the NTSC signal having frequency band of 4.2 MHz is about 450 TV's/effective scanning lines (horizontal resolution).
It is clear from the above mentioned numerical values that the HD signal contains information in both vertical resolution and horizontal resolution about 2.2 times that of the NTSC signals.
In order to record/reproduce such HD signal, a dedicated recording/reproducing apparatus such as 1/2-inch cassette High-Definition TV VTR (a standard established by Japan Broadcasting Corporation/NHK) or MUSE (Multiple Sub-Nyquist Sampling Encoding System)--VTR, etc., is necessary. On the other hand, there is a method of recording and reproducing the HD signal without using such dedicated apparatus. In such method, an HD signal is converted into a conventional video signal by means of, for example, an HD to NTSC converter or a MUSE to NTSC converter and the video signal thus converted is recorded/reproduced by means of a VTR of the conventional system.
It is well known that the 1/2-inch cassette High-Definition TV VTR or the MUSE-VTR, etc., dedicated to the HD signal is very complicated and expensive and can not record/reproduce the video signal of the conventional system.
In the method of recording and reproducing the HD signal without using such dedicated apparatus, in which an signal is converted into a conventional video signal by means of, for example, an HD to NTSC converter or a MUSE to NTSC converter and the video signal thus converted is recorded/reproduced by means of a VTR of the conventional system, it is impossible to record an original high definition signal or a wide image.